1. Field of the Invention
The present invention generally relates to flashing fixing devices wherein toners on media are fixed by flash lights and printing devices using the flash fixing devices. More particularly, the present invention relates to a flash fixing device, by which an unevenness of a light(brightness) and a shade(darkness) of a half tone picture can be reduced so that a toner image having a high resolution can be fixed, and a printing device using the flash fixing device.
2. Description of the Related Art
In the field of a printer forming a toner image using an electronic picture method or the like, a picture is formed on a printing medium by a powder toner. Hence, the powder toner on the printing medium is melted so as to fix the toner image. It is necessary for fixing the toner image to give fixing energy to the printing medium, for example.
In the field of high speed printers, a non-contact type fixing method is used for giving fixing energy. The non-contact type fixing method is proper for fixing the toner image of a high speed printer because high fixing energy can be given without adversely affecting the conveyance of the printing medium.
As a non-contact type fixing method, a flash fixing method, in which the flash light of a flash lamp is used, has been used. It is possible to fix the toner image in every designated area of the printing medium, by the flash fixing method wherein the flash lamp emits light with a designated time interval as corresponding to the conveyance of the printing medium.
In the above mentioned flash fixing method, it is efficient to fix the toner image for the designated area of the printing medium using one flash emission. However, generally, the emission energy distribution of the flash light is not uniform throughout the designated area of the printing medium. Therefore, the flash light is double-strikes (emits light twice) to a part of the designated area of the printing medium.
With regard to the double-striking of the flash light, there is related art to achieve a proper emission energy distribution and a proper double-strike area so as to avoid a fixing unevenness of a toner image, as disclosed in the Japanese Patent 2870705 or the Japanese Laid-Open Patent Application, No. 6-308852.
However, according to the above mentioned related art, in order to prevent the dispersion of a fixing ratio of the toner, the change of the emission energy distribution is controlled. That is, the above mentioned related art inventions have problems in that the emission energy in an entire area of a printing medium has to be controlled so as to have a higher value than a sufficient value to fix the toner and a lower value than an excessive value to cause the toner to be ruptured.
In the meantime, recently, it has been required to print not only a character but also a half tone picture, especially to print with a high resolution. In a case of printing with a high resolution such as 600 dpi, for example, as shown in FIG. 1, it is necessary to fix a toner having a smaller dot size than the dot size of a low resolution such as 240 dpi.
To improve such a high resolution, a difference of a dot diameter size after the toner is fixed becomes a problem. More particularly, in a case where the emission energy is given, the toner in the dot is melted so as to go out from the periphery of the primary dot. An area in the part where the toner goes out from the periphery of the dot, the going out area, varies based on the difference in the amount of the emission energy provided.
FIG. 1 is a view for explaining a cause an unevenness of light and shade that is a problem of the related art. As shown in FIG. 1, in a case where the emission energy is small, the going out area is small. In a case where the emission energy is large, the going out area is large. The above mentioned difference of the going out areas does not stand out in a case where the high resolution is approximately 240 dpi.
However, in a case where the high resolution of approximately 600 dpi, the size of the dot becomes less than a half size. Hence, a difference of the size of a dot diameter after fixing the toner does stand out because of the difference of the going out areas. Particularly, in a case of a half tone picture, there seems to be a different graduation resulting despite the same graduation originally.
In the above mentioned related art, the emission energy distribution sufficient to fix the toner is given to the continuous-form medium. Accordingly, with regard to the emission energy having a higher value than the above mentioned fixing energy, only the explosion of the toner is considered. However, the unevenness of light and shade after fixing based on the emission energy is not considered.
That is, in the related art, the emission energy distribution of the flash, a fixing width, and a duplicate width are determined so as to prevent unevenness of fixing. The change of the emission energy having a higher value is not considered. Therefore, it is difficult to prevent the unevenness of light and shade in high resolution printing.
Furthermore, an important property of the emission energy distribution by one time flash emission is the unevenness of light and shade, which can be prevented by duplicating the flash light plural times. That is, if property of the emission energy distribution by the one time flash emission is made proper, it is possible to prevent the unevenness of light and shade and to reduce emission frequency and energy consumption in a case where the double-strike area is reduced. In a case of an application wherein plural flash lamps are used, it is necessary to control the orientation of a light from the plurality of the flash lamps. Hence, it is difficult to realize an emission energy distribution that can prevent not only the fixing unevenness but also the unevenness of light and shade.
Accordingly, it is a general object of the present invention to provide a novel and useful flash fixing device and a printing device using the flash fixing device in which one or more of the problems described above are eliminated.
Another and more specific object of the present invention is to provide a flash fixing device having a plurality of flash lamps and a printing device using the flash fixing device so as to realize one time flash emission energy distribution that is useful in preventing not only the fixing unevenness but also the unevenness of light(brightness) and shade(darkness).
The above objects of the present invention are achieved by a flash fixing device configured to fix a toner image by a flash light, including a plurality of flash lamps arranged parallel to each other, and a reflection board including a plurality of side part reflection surfaces each facing from a side to the respective flash lamps, wherein in a case where a surface including two central axes of the two flash lamps arranged one at each end is defined as a standard surface, an acute angle against the standard surface is set to be decreased as the side part reflection surface is positioned closer to a center of the arrangement of the plurality of the flash lamps.
In the present invention, the plurality of the flash lamps may be arranged parallel to each other in a conveyance direction of a printing medium. A light emitted with a designated emission frequency by the flash lamp is reflected to an irradiation area by the reflection board. As the side part reflection surface is close to a center of an arrangement of the flash lamps, the emission energy distribution is substantially constant at a central part by setting an inclination angle (acute angle) against the standard surface small and is decreased at both end parts as having a distance from the central part. The above mentioned property of the emission energy distribution is useful in order to obtain a melt energy distribution being substantially constant in an irradiation area by overlapping the plurality of the flash lights.
The above mentioned reflection board may be a member wherein respective side part reflection surfaces and the respective upper part reflection surface are formed together with. Alternatively, the above mentioned reflection board may include a plurality of members formed independently corresponding to the plurality of the flash lamps. In addition, although the respective side part reflection surfaces of the reflection board are flat so as to manufacture the reflection board efficiently, the respective side part reflection surfaces of the reflection board may have a crooked surface and/or a curved surface.
Other object of the present invention is to provide a flash fixing device configured to fix a toner image by a flash light, including a plurality of flash lamps arranged parallel to each other, and a reflection board including a side part reflection surface and an upper part reflection surface that partially surround the flash lamp, as corresponding to the respective flash lamps, so that a light emitted by the flash lamps is reflected to an irradiation area, wherein an emission energy distribution obtained by a one time flash light of the flash lamps is substantially constant at a central part of the irradiation area and decreases gradually from the central part to both end parts of the irradiation area.
According to the present invention, it is possible to realize the emission energy distribution having a trapezoid type that is useful in order to obtain a melt energy distribution being substantially constant in an irradiation area by overlapping the plurality of the flash lights. The above mentioned irradiation area may be an area on the printing medium corresponding to an opening width between both ends of the reflection board.
Other object of the present invention is to provide a printing device configured to form a toner image of a medium carried at a designated conveyance speed, including image forming means for forming the toner image at the medium, a flash fixing device configured to fix the toner image by a flash light, including a plurality of flash lamps arranged parallel to each other, and a reflection board including a side part reflection surface facing from a side to the flash lamp as corresponding to the respective flash lamps, wherein in a case where a surface including central axes of the two flash lamps arranged one at each end is defined as a standard surface, an acute angle against the standard surface is set to be decreased as the side part reflection surface is positioned closer to a center of the arrangement of the plurality of the flash lamps.
According to the present invention, it is possible to realize uniformity of the melt energy distribution by using the fixing device realizing a property of the emission energy distribution of the trapezoid type. Hence, even in the case of a high tone picture having a high resolution, it is possible to obtain a high quality picture without unevenness of light and shade.
Other objects, features, and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.